Choose the correct statement.

Light is an electromagnetic wave. Its speed in vacuum is given by the expression

If $E$ and $B$ denote electric and magnetic fields respectively,which of the following is dimensionless?

The layer of the atmosphere that reflects low frequency $(LF)$ electromagnetic waves during day time only is

In a plane electromagnetic wave,the electric field oscillates sinusoidally at a frequency of $2.0 \times 10^{10} \; Hz$ and amplitude $48 \; V m^{-1}$.
$(a)$ What is the wavelength of the wave?
$(b)$ What is the amplitude of the oscillating magnetic field?
$(c)$ Show that the average energy density of the $E$ field equals the average energy density of the $B$ field. $[c = 3 \times 10^{8} \; m s^{-1}]$.

$A$ charged particle oscillates about its mean equilibrium position with a frequency of $10^{9} \,Hz$. The frequency of electromagnetic waves produced by the oscillator is . . . . . . .